I had rebalanced my portfolio to add more bonds about a year before the crash of 2008. I watched my holdings go down about 25%. I read that stock funds dipped about 30-40%, so I came out a little bit ahead. I remember a coworker panicking and he told me he was going to move everything over to some fixed account before he lost any more money. I told him, please, please don't do that for your sake. The stock market is not going to go to zero and you will recoup your losses if you hold on. Right now they are just paper losses, but if you cash out they are real losses. But he did it anyway.
Needless to say, I just kept investing at my usual 20% (Was not really planning for very early retirement, and didn't make enough to anyway), and my portfolio has more than doubled from what it was in 2007.
I learned a lot over the years having just started putting money in a 403B in September of 1987, just to watch it drop in October!
You have to be in it for the long haul. Miss Prim